The present invention relates to polyamide-based compositions, and more particularly, it relates to flame retarded polyamides prepared by adding melamine cyanurate and a polyol to the polyamides.
Polyamides have numerous uses because of their outstanding physical properties. Notwithstanding all this, in certain special areas, including among others the automobile, aerospace, and electrical industries, the use of polyamides has been limited by their excessive combustibility. To cure this problem, numerous solutions have already been proposed, but none of these has been found to be entirely satisfactory in practice.
Further, the customary fire retardant additives based on organic halogen derivatives, such as, for example, decabromodiphenyl ether, alone or in combination with antimony oxide, are producers of halogen acids which are released during fabrication or during the use of polyamides containing them. This results in corrosion risks to equipment and to environmental damage.
Phosphorus which has also been suggested, for example, in U.S. Pat. No. 3,778,407, is not easy to use and also causes a reddish tint in the polyamides to which it is added.
Some substantial progress has been made through the use of melamine cyanurate, as shown in French Patent documents Nos. 7923111 and 8204446 and European Pat. No. 0019768, but these compositions are not as effective on a weight basis as certain compounds with a high chlorine or bromine content.
On the other hand, it must not be lost sight of that even if the additives mentioned above reduce the combustion tendencies of the plastic materials in which they are incorporated, this tendency being measured by the Oxygen Index limit, according to French standard NFT 51.071 or ASTM D 2863, these prior art additives have no effect on the tendency to drip. This characteristic is also required of the above-cited materials by ASTM standard D 635 and by combustion test UL 94 described in Bulletin 94 of the Underwriters Laboratories.